Conventionally, oil supply apparatuses are known which supply engine oil (hereinafter, simply referred to as oil) to respective parts of an engine with an oil pump as oil for lubricating bearing sections and sliding sections of the engine, as oil for cooling pistons, or as oil for operating devices which are operated by oil pressure. For example, Patent Literature 1 discloses an oil supply apparatus configured to suppress a temperature rise of a piston or a cylinder by injecting oil to the piston from a jet nozzle during a high-load high-rotation operation of an engine. This oil supply apparatus includes a variable displacement oil pump and is configured to cause oil to be injected from the jet nozzle by controlling an on-off valve and cause a discharge amount of the oil pump to be increased in synchronization with the injection of oil during a high-load high-rotation operation of the engine. In other words, during oil injection from the jet nozzle, an oil discharge amount is increased to maintain overall oil pressure balance in oil supply paths in order to prevent a shortage of oil to be used for other purposes such as lubricating oil.
There is an intimate relationship between oil and fuel efficiency characteristics of an engine, and the lower the viscosity of oil used, the greater the improvement in fuel efficiency. This is because, as well known, oil with lower viscosity is more advantageous in terms of reducing sliding resistance at various parts of the engine.
However, quite a number of oils with relatively low viscosity have relatively low upper-limit operating temperatures. When an engine using such oil is operated at a high rotation and under a high load over an extended period of time, deterioration of the oil due to a rise in temperature (overheating) may conceivably cause galling of a sliding section or the like. Normally, since oil is selected by a user according to his or her preferences, inconveniences such as that described above are desirably prevented in advance in the engine. However, the conventional oil supply apparatus described above is not equipped with such countermeasures.